Variable exhaust mixing device

ABSTRACT

A system and method for variable exhaust mixing is provided. A variable exhaust mixing device including a butterfly valve is positioned in an exhaust stream and the butterfly valve is opened more to decrease mixing and closed more to increase mixing. The increased mixing provided by the variable exhaust mixing device allows the injection of dosed fuel into the exhaust stream at a lower exhaust flow rate.

BACKGROUND

A Diesel Oxidation Catalyst (DOC) uses a chemical process to break downpollutants from diesel engines in the exhaust stream, turning them intoless harmful components. The DOC is normally a honeycomb shapedconfiguration coated in a catalyst designed to trigger a chemicalreaction to reduce particulate matter. More specifically, a DOC is anexhaust aftertreatment device for diesel engines and contains palladiumand platinum which serve as catalysts to oxidize hydrocarbons and carbonmonoxide into carbon dioxide and water.

Additionally, dosed fuel may be provided to the DOC to improve DOCperformance. However, there are limitations on how much fuel can bedosed depending on exhaust flow and temperature

SUMMARY

A variable exhaust mixing system is provided that includes a butterflyvalve positioned in an exhaust stream. The butterfly valve is openedmore to decrease mixing and closed more to increase mixing. Theincreased mixing provided by the variable exhaust mixing device allowsthe injection of dosed fuel into the exhaust stream at a lower exhaustflow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a variable exhaust mixing system.

FIG. 2 illustrates the DOC inlet temperature, the Pre-DOC outtemperature, the Pre-DOC in temperature, and the engine speed in rpm.

DETAILED DESCRIPTION

FIG. 1 illustrates a variable exhaust mixing system 100. FIG. 1 includesa turbocharger 110, an exhaust stream 120, a variable exhaust mixingdevice 130, a device controller 140, a dosing valve 150, dosed fuel 160,and a Diesel Oxidation Catalyst (DOC) 170.

In operation, the exhaust stream 120 downstream of the turbocharger 110passes through a variable exhaust mixing device 130 that is controlledby a device control 140. The exhaust stream 120 continues to a dosingvalve 150 where dosed fuel 160 is provided to the exhaust stream 120before the exhaust stream 120 enters the DOC 170.

During operation, the variable exhaust mixing device 130 provides bettermixing of the dosed fuel into the exhaust flow, which allowssignificantly improved conversion in the DOC 170. As shown in FIG. 1,the variable exhaust mixing device is a piece of hardware placed in theexhaust system, downstream of the turbocharger and upstream of thedosing valve, which creates swirl in the exhaust.

In one embodiment, the variable exhaust mixing device 130 is a butterflyvalve placed in the exhaust stream, which may be commanded to open andclose to different positions. This valve improves the mixing of the fuelinto the exhaust stream and provides a wider range of engine operationwhere fuel may be injected. Additionally, the valve is controlled in anembodiment by software provided by the device controller 140.

Additionally, the variable exhaust mixing device allows the injection offuel at low flow.

FIG. 2 illustrates the DOC inlet temperature 210, the Pre-DOC outtemperature 220, the Pre-DOC in temperature 230, and the engine speed inrpm 240. The improved conversion due to the variable exhaust mixingdevice is shown in FIG. 2. More specifically, an approximately 90 Cadditional temperature out of the DOC was achieved under the sameconditions when using a mixing device.

With regard to the software control of the valve, in an embodiment, thevalve changes orientation based on engine operation. For example, lowexhaust flow is provided with more aggressive mixing (the butterflyvalve is closed more) which may not be possible at higher flows due tobackpressure, for example. Consequently, based on exhaust flow, thevalve is controlled to change its orientation to produce greater orlesser mixing.

Additionally, the ability to produce variable mixing increases theexhaust flow range in which fuel may be injected. For example, the fuelmay now be injected over the entire exhaust flow operating range asopposed to not being able to be injected at flows below about 300 kg/hr,for example.

Additionally, although a butterfly valve has been discussed above, othertypes of valves may be employed such as a gate valve or disc valve.Additionally, multiple types of valves may be employed.

1. A variable exhaust mixing system including: a variable exhaust mixingdevice positioned in an exhaust stream; wherein said variable exhaustmixing device is controlled to decrease the amount of mixing of saidexhaust stream with increasing exhaust flow.
 2. The system of claim 1wherein a device control controls said variable exhaust mixing device.3. The system of claim 1 wherein a dosing valve is present in theexhaust stream downstream of said variable exhaust mixing device.
 4. Thesystem of claim 3 wherein said dosing valve provides dosed fuel into theexhaust stream.
 5. The system of claim 1 wherein said variable exhaustmixing device is a butterfly valve.
 6. The system of claim 5 whereinsaid butterfly valve is opened more to decrease mixing
 7. The system ofclaim 5 wherein said butterfly valve is closed more to increase mixing.8. The system of claim 1 wherein said variable exhaust mixing device islocated downstream from a turbocharger.
 9. The system of claim 1 whereinsaid variable exhaust mixing device is located upstream of a DieselOxidation Catalyst (DOC).
 10. A method for producing variable mixing ofan exhaust stream, said method including: positioning a variable exhaustmixing device in an exhaust stream, wherein said variable exhaust mixingdevice is a butterfly valve.
 11. The method of claim 10 wherein saidbutterfly valve is opened more to decrease mixing
 12. The method ofclaim 10 wherein said butterfly valve is closed more to increase mixing.